Correlation between dc polarization and failure characteristics of XLPE and EPR aged with ac voltage in a wet environment

Polarization and depolarization currents obtained at a low de field for two different brands of XLPE and EPR insulation subjected to water treeing were correlated with the insulation breakdown characteristics to assess the diagnostic value of various polarization/depolarization current parameters. It is shown that for all three materials the polarization currents change more consistently with aging than do the depolarization currents. It is also shown that although the RC time constant and the area under the polarization current curve change consistently with the aging time for all three materials tested, the consistency and the diagnostic value of the information they provide about impending insulation failure depends very much on the type of material.